1. Field of the Invention
This invention relates generally to magnetic recording hard disk drives (HDDs), and more particularly to a HDD with high data track density that counts the number of writes to the data tracks to minimize the effect of adjacent track encroachment (ATE) during writing.
2. Description of the Related Art
HDDs with high data density are required to have high data track density, which means that the concentric data tracks are packed closer together. High track density increases the problem of adjacent track encroachment (ATE). ATE occurs when old data stored in tracks adjacent to the track being written become degraded after many writings to the data track. ATE generally translates into an increase in bit error rate (BER), resulting in degradation of the performance and reliability of the HDD.
One approach for addressing the ATE problem is to count the number of writes to each track. When a track has been written to a predetermined number of times, that track and one or more adjacent tracks on both sides of it are read and then rewritten. The effects of ATE cannot build up because significant repetitive writing of a single track is avoided. This approach is described in U.S. Pat. No. 7,567,400 B2, which is assigned to the same assignee as this application. However, because HDDs may have a very large number of tracks, e.g., several hundred thousand, a significant amount of memory may be required to be allocated to store the counts for each track.
Thus what is needed is a HDD that counts the writes to the data tracks in a manner that makes efficient use of memory and still effectively addresses the problem of ATE.